Method of making a reflective shield

ABSTRACT

A method of creating a reflective shield for an image sensor device includes depositing a first dielectric layer on a substrate, wherein a photodiode is on the substrate. The method further includes removing surface topography by performing chemical mechanical polishing (CMP) on the first dielectric layer. The method further includes patterning the substrate to define an area on a surface of the first dielectric layer, wherein the area is directly above the photodiode. The method further includes depositing a layer of a material with high reflectivity on the substrate, wherein the material fills the area on the surface of the first dielectric layer. The method further includes removing excess material with high reflectivity, wherein the reflective shield is formed and is embedded in the first dielectric layer. The method further includes depositing a second dielectric material on the substrate, wherein the second dielectric material covers the reflective shield.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No.12/761,736, filed Apr. 16, 2010, which is incorporated by referenceherein in its entirety.

FIELD

The present disclosure relates generally to semiconductor devices, andmore particularly, to image sensor devices.

BACKGROUND

Semiconductor image sensors are used for sensing radiation such aslight. Complementary metal-oxide-semiconductor (CMOS) image sensors(CIS) and charge-coupled device (CCD) sensors are widely used in variousapplications such as digital still camera or mobile phone cameradevices. These devices utilize an array of pixels in a substrate,including photodiodes and transistors that can absorb radiationprojected toward the substrate and convert the sensed radiation intoelectrical signals. The demands of higher resolution and lower powerconsumption have encouraged further miniaturization and integration ofthese image sensors. It is within this context the following disclosurearises.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, andlike reference numerals designate like structural elements.

FIG. 1 shows a simplified cross-sectional view of an active pixel cellthat uses four transistors, in accordance with some embodiments.

FIG. 2 shows a more detailed cross-sectional view of FIG. 1, inaccordance with some embodiments.

FIG. 3A shows an inserted reflective layer above the photodiode, inaccordance with some embodiments.

FIG. 3B shows a concave inserted reflective layer above the photodiode,in accordance with some embodiments.

FIGS. 3C (a) and (b) show reflective layers being used to reflect lightpassing through photodiodes, in accordance with some embodiments.

FIGS. 4A-4F illustrate structures and intermediate stages in a processflow for creating a reflective shield above a photodiode, in accordancewith some embodiments.

FIG. 4G shows a cross sectional diagram of an active pixel cell with thereflective layer 300 at the top surface of the PMD (pre-metaldielectric) layer, in accordance with some embodiments.

FIGS. 5A-5J illustrate structures and intermediate stages in a processflow for creating a concave reflective shield above a photodiode, inaccordance with some embodiments.

FIGS. 6A-6H illustrate top views of reflective shields abovephotodiodes, in accordance with some embodiments.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof the disclosure. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 shows a simplified cross-sectional view of an active pixel cell100 that uses four transistors, in accordance with some embodiments.Such active pixel cell may also be called as a 4T pixel cell. 4T pixelcell 100 includes a photodiode PD, a transfer transistor T1, a resettransistor T2, a source-follower (“SF”) or amplifier (“AMP”) transistorT3, and a row select (“RS”) transistor T4.

During operation, transfer transistor T1 receives a transfer signal TX,which transfers the charge accumulated in photodiode PD to a floatingdrain/diffusion node FD. Reset transistor T2 is coupled between a powerrail VDD and the node FD to reset the pixel (e.g., discharge or chargethe FD and the PD to a preset voltage) under control of a reset signalRST. The node FD is coupled to control the gate of AMP transistor T3.AMP transistor T3 is coupled between the power rail VDD and RStransistor T4. AMP transistor T3 operates as a source-follower providinga high impedance connection to the floating diffusion FD. Finally, RStransistor T4 selectively couples the output of the pixel circuitry tothe readout column line under control of a signal RS. In someembodiments, the photodiode PD of a pixel cell is passivated with ashallow pinning layer (not shown) to reduce surface defects. In thisexample, an N type PD is implanted into a P-epitaxial layer, the pinningis formed by a shallow P type implant. Other types of photodiodes canalso be used.

The demand for higher image quality, such as digital-still-camera-like(or DSC-like) quality for mobile applications, requires decreasing pixelsize while maintaining full-well capacity, quantum efficiency, andsensitivity. To meet such demands becomes very challenging. With thedecreased pixel size, the total absorption depth becomes insufficientfor some light, especially for long-wavelength light, and for imagesensors using backside illumination (BSI) technology. In someembodiments, the width of CIS using BSI is between about 0.1 μm andabout 2 μm.

FIG. 2 shows a more detailed cross-sectional view of FIG. 1, inaccordance with some embodiments. FIG. 2 shows a gate 201 of transfertransistor T1, a gate 202 of reset transistor T2 and a photodiode 205next to the gate 201 of transfer transistor T1. The transfer transistorT1 and the reset transistor T2 share a floating diffusion region (FD)204 and the image sensor 200 is separated from other image sensors byshallow trench isolations 235 and 236. In some embodiments, eachtransistor, such as transistors T1 and T2, has a gate dielectric layer215 and spacers 214. FIG. 2 shows that an N type doped layer 216 isimplanted into a P-epitaxial layer 220. However, structures and methodsfor improving quantum efficiency described in this disclosure are notlimited to the type of photodiodes described here. Other types ofphotodiodes, such as P-type photodiodes, can also be used. The pixel 200is built on a substrate 230.

There are contact plugs 208, 210, 209, and 211 above gate 201 oftransfer transistor T1, gate 202 of reset transistor T2, diffusionregion 204 and diffusion region 207 respectively to provideinterconnection. The contact plugs 208, 210, 209, and 211 are surroundedby an inter-level dielectric (ILD) layer 213. Image sensor 200, receivesphotons 250 from the backside of substrate 230 (back side illumination),as shown in FIG. 2. Due to shrinking of the pixel size (or the size ofimage sensor 200, which is a pixel), the area of photodiode 205 has beendecreased. As a result, the number of photons 250 that are available tohit the photodiode 205 have decreased. Therefore, higher absorption rateof impeding photons 250 is required. For backside illumination (BSI)technology, the total absorption depth 240 could be insufficient forlong-wavelength rays, such as red light. FIG. 3A shows a reflectivelayer 310 (or a reflective shield) being inserted in the ILD layer 213above the photodiode 205 to reflect the light that has passed photodiode205 without being absorbed, in accordance with some embodiments. FIG. 3Ashows that photon 350 has been reflected by a surface 311 of thereflective layer 310 and been redirected toward the photodiode 205.Photon 350 is one of photons 250 hitting photodiode 205 from thebackside of substrate 230. The reflected photon 350 can be absorbed bythe photodiode 205 when it travels through the absorption depth 240 ofphotodiode 205. The absorption length for photon 350 can be at leastdoubled due to the reflective layer 310. Therefore, the absorptionefficiency (or quantum efficiency) is increased due to the insertion ofthe reflective layer (or shield) 310.

The reflective layer 310 in FIG. 3A has a flat surface 311, which isparallel to the surface 312 of photodiode 205. Alternatively, thesurface of the reflective layer 310 can be concave to direct the photonstoward the photodiode 203. FIG. 3B shows a concave reflective layer 310′being inserted in the ILD layer 213 above the photodiode 205 to reflectthe light that has passed photodiode 205 without being absorbed, inaccordance with some embodiments. FIG. 3B shows that a photon 350′ isreflected by a concave surface 311′ of the reflective layer 310′ and isredirected toward the center of photodiode 205. Since surface 311′ isconcave, surface 311′ is able to direct light impeding the reflectivelayer 310′ (or more precisely surface 311′) at an angle θ that rangesbetween zero and substantially non-zero toward the photodiode 205.

FIGS. 3C (a) and (b) show the two reflective layers 310 and 310′ ofFIGS. 3A and 3B respectively, in accordance with some embodiments. FIG.3A (a) shows the reflective layer 310 having a flat surface 311 thatfaces and is parallel to the surface 312 of photodiode 205. When animpeding photon 351 arrives at the reflective layer 310 at an angle α,the photon is reflected off the surface 311 also at an angle α. Theangle α ranges from zero to substantially non-zero (from the normal ofsurface 312). In the example shown in FIG. 3C (a), due to the location320 and the angle α the photon 351 hits, the reflected photon 351 landsoutside the surface 312 of photodiode 205 and cannot be absorbed byphotodiode 205. However, when photon 351′ hits a concave surface 311′ ofFIG. 3C (b) at an angle α from the normal of surface 312, the reflectedphoton 351′ leaves concave surface 311′ at an angle β to the normal ofsurface 312. Since angle β is smaller than angle α, due the concavesurface 311′, the photon 351′ falls inside surface 312 of photodiode 205and can be absorbed by photodiode 205. Concave surface 311′ is capableof directing more photons arriving at the reflective layer that are notsubstantially perpendicular to the surfaces of the photodiodes (orarriving at a non-zero angle) toward the surface of photodiodes to beabsorbed.

FIGS. 4A-4F illustrate structures and intermediate stages in a processflow for preparing an image sensor with an inserted reflective layer, inaccordance with some embodiments. FIG. 4A shows that gate 201 and gate202 have been prepared on a substrate 400, in accordance with someembodiments. As described above in FIGS. 1, 2, 3A and 3B, gate 201 isthe transfer gate T1 and gate 202 is the reset gate T2. After thetransistors T1 and T2 have been prepared, a first inter-level dielectric(ILD) layer 401 is deposited. The first ILD layer 401 can be made of anydielectric material, such as silicon dioxide (or undoped silicon glassUSG), silicon nitride, or a combination of both films. The first ILDlayer 401 may also be a doped dielectric film, such as BPSG (boron andphosphorous doped silicon glass) or PSG (phosphorous doped siliconglass), a low-dielectric-constant (low-K) material, such asfluorine-doped silicon glass (FSG) or other low-K materials used insemiconductor device manufacturing. One example of a material for thefirst ILD layer 401 is silicon oxide deposited by plasma enhancedchemical vapor deposition (PECVD) using TEOS (Tetraethyl orthosilicate)as the silicon source. PECVD silane oxide film can also be used. In someembodiments, the TEOS oxide has a thickness between about 3000 Å toabout 15000 Å. The first ILD layer 401 does not need to be deposited byPECVD. The dielectric layer 101 can be a spin-on dielectric (SOD) or aspin-on glass (SOG). The first ILD layer 401 may also be deposited byhigh-density plasma chemical vapor deposition (HDPCVD), orsub-atmosphere chemical vapor deposition (SACVD). Other types ofdielectric deposition processes may also be used.

The deposited ILD 401 has surface topography resulting from thestructures on the substrate. In some embodiments, the surface topographyis removed by chemical mechanical polishing (CMP), which has thecapability of globally planarizing a substrate surface. The depositedILD 401 has a minimal thickness of the height “H” of the gatestructures, such as gates T1 and T2. In addition, a certain amount ofILD “T_(min)” needs to remain above the gate to ensure that polishingpad of CMP does not come in contact with any gate structures on thesubstrate to damage the gates. In some embodiments, T_(min) is betweenabout 100 Å and about 5000 Å. In some embodiments, the total thicknessof H and T_(min) is kept as small as possible to prevent absorptionand/or diffraction of light in the ILD film, and to maintain theintensity of light reflected by the inserted reflective layer, such aslayers 310 and 310′ of FIGS. 2 and 3A-3C, to be formed.

Afterwards, the substrate is patterned and etched to create an openedarea (or opening) 402 to deposit the reflective layer 310 describedabove, as shown in FIG. 4B in accordance with some embodiments. Afteropened area 402 is created, a reflective material (or a material withhigh reflectivity) is deposited on the substrate surface and fills theopened area 402. Reflectivity is defined as a fraction of impeding lightbeing reflected. A reflective material can reflect a fraction (orpercentage) of impeding light, such as 5%, 10%, 50% or 80%. The higherthe reflectivity of the material, the higher percentage of the impedinglight is reflected. Most of the metals have relatively highreflectivity. In some embodiments, the reflective materials for theapplications described above are metals. Examples of reflective metalsthat can be used for such application include, but are not limited to,tungsten (W), aluminum (Al), and copper (Cu), zinc (Zn, gold (Au),silver (Ag), titanium (Ti), tantalum (Ta), chromium (Cr), tin (Sn),cobalt (Co), and nickel (Ni). The reflective material can also be ametal-containing film or an alloy that is made of two or more metals.

Non-metal (or non-metallic) materials that are reflective may also beused. For example, polytetrafluorethylene (PTFE) is a polymer that hashigh reflectivity. In some embodiments, an adhesion layer (oradhesion-promoting layer) (not shown here) is deposited under thereflective layer to promote adhesion between the reflective layer andILD. For example, if the reflective layer 310 is made of W, an adhesionlayer made of Ti, TiN, Ta, TaN, or a combination of the above-mentionedadhesion-promoting materials can be used. FIG. 4C shows a metal film403, such as W, and an optional adhesive layer (not shown) deposited onthe substrate, in accordance with one embodiment of this disclosure. Thereflective material can be deposited by CVD, physical vapor deposition(PVD), atomic layer deposition (ALD), plating, spin-on or otherapplicable methods. For example, W can be deposited by CVD.Adhesion-promoting material for W, such as Ti and TiN, can be depositedby PVD in some embodiments. In some embodiments, the reflective materialis selectively deposited in the opened area 402. In some embodiments,the metal film 403 deposited has a thickness between about 200 Å andabout 5000 Å. In some embodiments, the adhesion layer deposited has athickness between about 10 Å and about 500 Å.

After the deposition of the reflective material, the excess reflectivematerial on the substrate surface is removed, such as by CMP, and leavesonly the reflective material only in opened area 402. CMP is not theonly method that can be used to remove excess material. In someembodiments, the excess reflective material can be removed by etchingprocess(es), which could be dry or wet. If an adhesion layer has beendeposited under the reflective material, the adhesion layer not in theopened area 402 is also removed. FIG. 4D shows substrate 400 after theremoval of reflective material from the substrate surface and leaves thereflective layer 310 (or reflective shield) on the substrate surface. Insome embodiments, the thickness of reflective layer 310 is greater thanabout 200 Å. In some other embodiments, the thickness of reflectivelayer 310 is greater than about 500 Å. In yet other embodiments, thethickness of reflective layer 310 is between about 100 Å to about 2000Å.

Afterwards, a second ILD layer 404 is deposited. The second ILD layer404 can be made of the same material as ILD layer 401, or differentmaterial from ILD layer 401. The materials and deposition methodsmentioned above for ILD layer 401 can be used for ILD layer 404. In oneembodiment, the second ILD layer 404 is an oxide deposited from silaneor TEOS, and has a thickness between about 500 Å and about 10000 Å. Inanother embodiment, the second ILD layer 404 has a thickness betweenabout 1000 Å and about 5000 Å. FIG. 4E shows substrate 400 after thesecond ILD layer 404 is deposited, in accordance with one embodiment ofthis disclosure. The reflective layer 310 is sandwiched between thefirst ILD layer 401 and the second ILD layer 404. The first ILD layer401 and the second ILD layer 404 make up a pre-metal dielectric layer(or PMD layer).

After the deposition of the second ILD layer 404, the substrate ispatterned to create openings for contact plugs, such as plugs 208, 209,210, and 211, and to fill such contact openings with adhesion layer andcontact metal. In some embodiments, the contact metal is W and theadhesion layer is made of Ti, TiN, Ta, TaN, or a combination of theabove-mentioned barrier materials. Additional processing operations,such as operations needed to establish additional levels ofinterconnection, are needed to complete the manufacturing of the imagesensors on the substrate. In some embodiments, the second ILD layer 404does not exist and the reflective layer 310 resides at the top surface(or interface) of the PMD layer. Under such circumstances, the contactplugs can be patterned right after or right before the opening 402 (theopening for the reflective layer) is created, in accordance with someembodiments. The adhesion layer and contact gap-fill layer can also beused to fill opening 402 (to create the reflective layer), in accordancewith some embodiments. FIG. 4G shows a cross sectional diagram of anactive pixel cell with the reflective layer 300 at the top surface ofthe PMD layer, in accordance with some embodiments. In FIG. 4G, thematerials used to fill the contact plugs, such as the adhesion layer andthe contact metal, are also used to create the reflective layer.

The embodiment of process flow described above in FIGS. 4A-4F can beused to create a reflective layer (or shield) to reflect light that isnot absorbed by photodiodes back to photodiodes for additionalabsorption. The reflective layer (or shield) created has a flat surfacefacing the photodiode (or a surface parallel to the surface of thephotodiode). As mentioned in FIGS. 3B and 3C, the surface of thereflective layer facing the photodiode can be concave to help directreflected light toward the surface of the photodiode. FIGS. 5A-5Jillustrate structures and intermediate stages in a process flow forpreparing an image sensor with an inserted reflective layer, inaccordance with some embodiments.

FIG. 5A shows that gate 201 and gate 202 have been prepared on asubstrate 500, in accordance with one or more embodiments. The gatestructures T1 and T2 of FIG. 5A are similar to the gate structures T1and T2 described in FIG. 4A-4F. As described above in FIG. 4A, aftertransistors T1 and T2 have been prepared, a first inter-level dielectric(ILD) layer 501 has been deposited. The possible materials andmanufacturing methods for the first ILD layer 501 are similar to thematerials and manufacturing methods of the first ILD layer 401.

The deposited ILD 501 has surface topography resulting from thestructures on the substrate. The surface topography is removed bychemical mechanical polishing (CMP), in some embodiments. Similar toFIG. 4A, the deposited ILD 501 has a minimal thickness of the height “H”of the gate structures, such as gates T1 and T2. In addition, a certainamount of ILD “T_(min)” needs to remain above the gate to ensure thatpolishing pad of CMP does not come in contact with any gate structureson the substrate to damage the gates. In some embodiments, T_(min)between about 100 Å and about 5000 Å. In one embodiment, the totalthickness of H and T_(min) is kept as small as possible to preventabsorption and/or diffraction of light in the ILD film, and to maintainthe intensity of light reflected.

Afterwards, the substrate is patterned with a photoresist layer 511, asshown in FIG. 5B in accordance with some embodiments. The photoresistlayer 511 is disposed over an area for creating the opened area (oropening, 502 in FIG. 5E described below). Photoresist layer 511 istreated to create a concave shape, as shown in FIG. 5C. In someembodiments, the treatment to create the concave-shaped photoresist 511′can be a low temperature reflow (or bake, or curing), at a temperaturebetween about 100° C. to about 300° C. for a duration between 0.1minutes and about 10 minutes. In some other embodiments, the treatmentcan be implanting molecules into the photoresist to harden thephotoresist 511 of FIG. 5B.

After the dome-shaped photoresist 511′ is formed, another photoresistlayer 512 is applied on the substrate and patterned to cover areas thatare not covered by the dome-shaped photoresist 511′, as shown in FIG. 5Din accordance with some embodiments. Afterwards, the dome-shapedphotoresist 511′, which has been hardened, is etched to leave adomed-shaped opening 502 in the first ILD layer 501, as shown in FIG. 5Ein accordance with some embodiments. FIGS. 5D and 5E show that a portion“P” of photoresist layer 512 is removed during the etching of thedome-shaped photoresist 511′ and the first ILD layer 510 under thedome-shaped photoresist 511′. Afterwards, the remaining photoresistlayer 512 is removed, as shown in FIG. 5F in accordance with someembodiments.

Following the removal of photoresist layer 512, a reflective material isdeposited on the substrate surface and fills the opened area 502. Thepotential reflective materials and deposition methods that can be usedfor this application are similar to those described above for theapplication for flat reflective layer 310 of FIGS. 4C and 4D. FIG. 5Gshows a metal layer 503, such as a W film, and an optional adhesivelayer (not shown) deposited on the substrate, in accordance with someembodiments.

After the deposition of the reflective material, the excess reflectivematerial on the substrate surface is removed, leaving only thereflective layer 310′ in opened area 502. For example, if the reflectivematerial is W, CMP can be used to remove the excess material. Asmentioned above, CMP is not the only method that can be used to removeexcess material. In some embodiments, the excess reflective material canbe removed by etching process(es), which could be dry or wet. If anadhesion layer has been deposited under the reflective material, theadhesion layer not in the opened area 502 is also removed. FIG. 5H showssubstrate 500 after the removal of reflective material from thesubstrate surface leaving the domed-shaped reflective layer 310′ (ordome-shaped reflective shield) on the substrate surface. In someembodiments, the smallest thickness of reflective layer 310′ is greaterthan about 200 Å. In some other embodiments, the smallest thickness ofreflective layer 310 is greater than about 500 Å. In yet otherembodiments, the thickness of reflective layer 310 is between about 100Å and about 2000 Å.

Afterwards, a second ILD layer 504 is deposited in accordance with someembodiments. The second ILD layer 504 can be made of the same ordifferent material as ILD layer 501. The materials and depositionmethods mentioned above for the first ILD layer 501 can be used for thesecond ILD layer 504. In some embodiments, the second ILD layer 404 isan oxide deposited from silane or TEOS, and has a thickness betweenabout 500 Å and about 10000 Å. In another embodiment, the second ILDlayer 504 has a thickness between about 1000 Å and about 5000 Å. FIG. 51shows substrate 500 after the second ILD layer 504 is deposited, inaccordance with some embodiments.

After the deposition of the second ILD layer 504, the substrate ispatterned to create openings for contact plugs, such as plugs 208, 209,210, and 211, and to fill such contact openings with adhesion layer andcontact metal. In some embodiments, the contact metal is W and theadhesion layer is made of Ti, TiN, Ta, TaN, or a combination of theabove-mentioned barrier materials. Additional processing operations,such as operations needed to establish additional levels ofinterconnection, are needed to complete the manufacturing of the imagesensors on the substrate.

The various embodiments of methods described above are for creating thereflective layer (or shield), such as layer 310 or 310′, for reflectinglight that is not absorbed by the photodiodes back toward thephotodiodes for additional absorption to increase the quantum efficiencyof photodiodes. Ideally, the size of the reflective shield should coverthe surface area of the photodiode and the photodiode's surroundingareas as much as possible to collect as much non-absorbed light toreflect back to the surface of the photodiode. However, since there areneighboring contact plugs, a minimal distance between reflective shield,such as shield 310 and 310′ described above in FIGS. 2, 3A-3C, 4D-4F,and 5H-5J, and the neighboring contact plugs, such as plug 208 toprevent shorting between the two neighboring structures.

FIG. 6A shows a top view of a reflective shield (or layer) 610 coveringa photodiode 605, in accordance with some embodiments. The photodiode605 and the reflective shield 610 could be rectangular or square-shaped,in some embodiments. The photodiode 605 does not need to be rectangular,and can be other shapes. In FIG. 6A, the reflective shield 610 is largerthan the photodiode 605 and covers the entire photodiode 605. In someembodiments, the reflective shield 610′ is smaller than the photodiode605, as shown in FIG. 6B. FIG. 6C shows a top view of a reflectiveshield 611 covering at least a portion of the photodiode 605′, inaccordance with some embodiments. The reflective shields 610′ and 611 donot cover the entire photodiode 605 possibly due to structures (notshown) neighboring the edges 606 and 607 of the photodiode 605.

FIG. 6D shows a top view of a circular reflective shield 612 coveringthe photodiode 605, in accordance with some embodiments. In addition tocircular and rectangular shapes, other shapes of reflective shields arealso possible. FIG. 6E shows a top view of a reflective shield 613covering a photodiode 605″, in accordance with some embodiments. Asmentioned above, the reflective shield and the photodiode can be in anyshape. The reflective shield 613 and the photodiode 605′ shown in FIG.6E are not in rectangular shapes or in circular shapes. There is anopening in one corner of each structure.

The reflective shields described above are all continuous pieces. Insome embodiments, the reflective shields can be separated into smallerpieces with small openings between the pieces. There could bemanufacturing concerns, such as dishing as a result of CMP, orelectrical concerns that would require the reflective shields be dividedinto smaller pieces. FIGS. 6F, 6G, and 6H show various embodiments ofreflective shields 614, 615, and 616 over the photodiode 605. In someembodiments, the space between the pieces is kept as small as possibleto prevent light from going through the space without being reflected.In some embodiments, the space between the pieces is between about 0.01μm and about 0.1 μm.

In some embodiments, the widths of reflective layers 310, 310′ arebetween about 0.1 μm to about 5 μm. In some other embodiments, thewidths of reflective layers 310, 310′ are between about 0.5 μm and about2.0 μm. In some embodiments, the lengths of reflective layers 310, 310′are between about 0.1 μm and about 10 μm. In some other embodiments, thewidths of reflective layers 310, 310′ are between about 0.5 μm and about4.0 μm.

The structures of reflective shields and methods of making suchstructures described enable reflection of light that has not beenabsorbed by photodiodes in image sensor devices and increase quantumefficiency of the photodiodes. Such structures can be applied (or used)for any image sensors to improve image quality. Such structures areparticular useful for image sensors with smaller pixel sizes and forlong-wavelength light (or rays), whose absorption length (or depth)could be insufficient, especially for BSI devices. The reflectiveshields could double, or more than double, the absorption depth forlight passing through the image sensors and getting reflected back tothe photodiodes. Concave-shaped reflective shields have the additionaladvantage of directing reflected light toward the image sensors.

One aspect of this description relates to a method of creating areflective shield for an image sensor device. The method includesdepositing a first dielectric layer on a substrate, wherein a photodiodeis on the substrate, and the first dielectric layer is in contact withthe photodiode. The method further includes removing surface topographyof the substrate by performing chemical mechanical polishing (CMP) onthe first dielectric layer. The method further includes patterning thesubstrate to define an area on a surface of the first dielectric layerafter CMP for the reflective shield, wherein the area defined for thereflective shield is directly above the photodiode. The method furtherincludes depositing a layer of a material with high reflectivity on thesubstrate after patterning the substrate, wherein the material with highreflectivity fills the area on the surface of the first dielectriclayer. The method further includes removing excess material with highreflectivity after the layer of the material with high reflectivity isdeposited, wherein the reflective shield is formed and is embedded inthe first dielectric layer. The method further includes depositing asecond dielectric material on the substrate, wherein the seconddielectric material covers the reflective shield.

Another aspect of this description relates to a method of creating areflective shield for an image sensor device. The method includesforming a first dielectric layer on a substrate, wherein a photodiode ison the substrate, and the first dielectric layer is in contact with thephotodiode. The method further includes patterning the first dielectriclayer to define an area for the reflective shield, wherein the areadefined for the reflective shield is directly above the photodiode, andthe area comprises at least two sub-areas spaced apart from one another.The method further includes forming a high reflectivity layer on thesubstrate, wherein the high reflectivity layer fills the defined area,and the high reflectivity layer is embedded in the first dielectriclayer. The method further includes forming a second dielectric materialon the substrate, wherein the second dielectric material covers the highreflectivity layer.

Still another aspect of this description relates to a method of creatinga reflective shield for an image sensor device. The method includesforming a first dielectric layer on a substrate, wherein a photodiode ison the substrate. The method further includes forming a photoresistmaterial over an area of the first dielectric layer, wherein the area isdirectly over the photodiode. The method further includes treating thephotoresist material to form a curved photoresist layer. The methodfurther includes forming a curved opening in the first dielectric layerusing the curved photoresist layer. The method further includes forminga high reflectivity layer on the substrate, wherein the highreflectivity layer fills the curved opening, wherein the highreflectivity layer includes at least two sub-areas spaced apart from oneanother.

Various modifications, changes, and variations apparent to those ofskill in the art may be made in the arrangement, operation, and detailsof the methods and systems disclosed. Although the foregoing disclosurehas been described in some detail for purposes of clarity ofunderstanding, it will be apparent that certain changes andmodifications may be practiced. Accordingly, the present embodiments areto be considered as illustrative and not restrictive, and the inventionis not to be limited to the details given herein, but may be modifiedwithin the scope and equivalents of the disclosure.

What is claimed is:
 1. A method of creating a reflective shield for animage sensor device, comprising: depositing a first dielectric layer ona substrate, wherein a photodiode is on the substrate, and the firstdielectric layer is in contact with the photodiode; removing surfacetopography of the substrate by performing chemical mechanical polishing(CMP) on the first dielectric layer; patterning the substrate to definean area on a surface of the first dielectric layer after CMP for thereflective shield, wherein the area defined for the reflective shield isdirectly above the photodiode; depositing a layer of a material withhigh reflectivity on the substrate after patterning the substrate,wherein the material with high reflectivity fills the area on thesurface of the first dielectric layer; removing excess material withhigh reflectivity after the layer of the material with high reflectivityis deposited, wherein the reflective shield is formed and is embedded inthe first dielectric layer; and depositing a second dielectric materialon the substrate, wherein the second dielectric material covers thereflective shield.
 2. The method of claim 1, wherein the method furthercomprises forming contact plugs to transistors near the photodiode. 3.The method of claim 1, wherein patterning the substrate to define anarea on a surface of the first dielectric layer includes patterning afirst photoresist, etching the first dielectric layer not covered by thepatterned first photoresist, and removing remaining portions of thefirst photoresist after etching the first dielectric layer.
 4. Themethod of claim 1, wherein the material with high reflectivity isselected from a group consisting of tungsten (W), aluminum (Al), andcopper (Cu), zinc (Zn, gold (Au), silver (Ag), titanium (Ti), tantalum(Ta), chromium (Cr), tin (Sn), cobalt (Co), nickel (Ni), and alloys madethereof.
 5. The method of claim 1, wherein the layer of the materialwith high reflectivity deposited has a thickness between about 100 Å andabout 2000 Å.
 6. The method of claim 1, wherein an adhesion layer isdeposited between the first dielectric layer and the layer of thematerial with high reflectivity, and wherein a thickness of the adhesionlayer is between about 10 Å and about 500 Å.
 7. The method of claim 1,wherein the first dielectric layer has a thickness between about 3000 Åand about 15000 Å.
 8. The method of claim 3, further comprising:treating the first photoresist after the first photoresist is patternedto make the first photoresist become dome-shaped; patterning a secondphotoresist after the first photoresist is treated, wherein the secondphotoresist is patterned to cover areas not covered by the patternedfirst photoresist; etching the substrate after the second photoresist ispatterned, wherein an opening with a concave surface facing thephotodiode is created in the first dielectric layer.
 9. The method ofclaim 1, wherein the area defined for the reflective shield has a widthbetween about 0.5 Åm and about 2 Åm.
 10. The method of claim 1, whereinthere is more than one area defined for the reflective shield above thephotodiode.
 11. The method of claim 1, wherein the reflective shield isadapted to reflect light coming from a back surface of the substratethat passes through the photodiode to re-enter the photodiode, andwherein the reflective shield increases an absorption length of thelight and a quantum efficiency of the photodiode.
 12. A method ofcreating a reflective shield for an image sensor device, the methodcomprising: forming a first dielectric layer on a substrate, wherein aphotodiode (PD) is on the substrate, and the first dielectric layer isin contact with the photodiode; patterning the first dielectric layer todefine an area for the reflective shield, wherein the area defined forthe reflective shield is directly above the photodiode, and the areacomprises at least two sub-areas spaced apart from one another; forminga high reflectivity layer on the substrate, wherein the highreflectivity layer fills the defined area, and the high reflectivitylayer is embedded in the first dielectric layer; and forming a seconddielectric material on the substrate, wherein the second dielectricmaterial covers the high reflectivity layer.
 13. The method of claim 12,wherein forming the first dielectric layer comprises forming the firstdielectric layer comprising at least one of silicon dioxide, undopedsilicon glass (USG) or silicon nitride.
 14. The method of claim 12,wherein forming the first dielectric layer comprises forming the firstdielectric layer using plasma enhanced chemical vapor deposition(PECVD), a spin-on process, high-density plasma chemical vapordeposition (HDPCVD), or sub-atmosphere chemical vapor deposition(SACVD).
 15. The method of claim 12, wherein forming the firstdielectric layer comprises forming the first dielectric layer having athickness over an active device on the substrate, and patterning thefirst dielectric layer comprises patterning the first dielectric layerhaving the thickness over the active device ranging from about 100angstroms (Å) to about 5000 Å.
 16. The method of claim 12, whereinpatterning the first dielectric layer comprises: forming a curvedphotoresist material over the defined area; and etching the curvedphotoresist material and the first dielectric layer.
 17. The method ofclaim 16, wherein forming the curved photoresist material comprises:forming a photoresist layer over the first dielectric layer; removingthe photoresist layer outside the defined area; and treating thephotoresist layer in the defined area to form the curved photoresistmaterial.
 18. The method of claim 17, wherein treating the photoresistlayer comprises heating the photoresist layer at a temperature rangingfrom about 100° C. to about 300° C. for a duration ranging from about0.1 minutes to about 10 minutes.
 19. A method of creating a reflectiveshield for an image sensor device, the method comprising: forming afirst dielectric layer on a substrate, wherein a photodiode (PD) is onthe substrate; forming a photoresist material over an area of the firstdielectric layer, wherein the area is directly over the photodiode;treating the photoresist material to form a curved photoresist layer;forming a curved opening in the first dielectric layer using the curvedphotoresist layer; and forming a high reflectivity layer on thesubstrate, wherein the high reflectivity layer fills the curved opening,wherein the high reflectivity layer includes at least two sub-areasspaced apart from one another.
 20. The method of claim 19, whereintreating the photoresist layer comprises heating the photoresist layerat a temperature ranging from about 100° C. to about 300° C. for aduration ranging from about 0.1 minutes to about 10 minutes.